1. Field of the Invention
The present invention relates to an access control device, a wireless device and a network, and is applicable to an access control device which assures communication quality at a wireless device on a network which is structured to include a plurality of wireless devices connecting with wireless terminals, to the wireless device equipped with this access control device, and to the network.
2. Description of the Related Art
Heretofore, at, for example, a wireless LAN access point according to an IEEE 802.11 specification, communications are carried out by ‘best effort’. Consequently, when performing real-time communications such as VoIP communications or the like, a bandwidth which is necessary to assure communication quality may not be obtained, which is a cause of a deterioration in quality.
In response to this problem, IEEE 802.11e has been established as a standard for assuring communication quality (quality of service, QoS), and assurance of communication quality is carried out in accordance therewith.
Under IEEE 802.11e, in order to support QoS, an access control procedure which extends the MAC layer has been standardized. As this access control procedure, an HCF (hybrid coordination function) function is prescribed. This HCF is a function integrated combining the functions of DCF (distributed coordination function), which is a conventional autonomous distributed access control procedure, and PCF (point coordination function), which is a centralized control section employing polling. HCF is principally divided into an HCF competitive channel access control format and an HCF controlled channel access control format.
The HCF competitive channel access control format is an improvement of the previous CSMA/CA procedure, categorizes transmission frames into categories in accordance with service quality, and applies priority control with differentials based on the service qualities of the respective categories.
The HCF controlled channel access control format is a procedure which extends conventional PCF, enables negotiations about communication quality between access points and terminals prior to data transfers and, in order to implement scheduling in consideration of predetermined qualities in accordance with data types when performing polling for data transfers, guarantees parameters such as a specified bandwidth, delay period and the like.
An example of a previously known technology is Japanese Patent Application Laid-Open (JP-A) No. 2004-304648.
As a number of connected client terminals become larger, sharing communication bandwidth between access points becomes complicated, and maintaining communication quality becomes difficult. In particular, assuring communication quality for access points that are performing communications which require real time behavior, such as VoIP communications, is strongly desired.
In such a case, ordinarily, a number of access point devices are increased, connections of client terminals which are currently connected are temporarily cut off, and those client terminals are caused to communicate with other access points using different channels.
However, a method to determine which access point a client terminal should be connected with when transferred to a connection with another access point is not standardized in IEEE 802.11. Therefore, if access points are implemented with the above-described standards technology of IEEE 802.11e as it is, a situation arises in which a client terminal will connect to only one of a plurality of access points, because of specifications of the client terminal (for example, a specification relating to networks which the client terminal requests connection to), variations in electromagnetic wave quality from fabrication of the access points, communications channels of the access points and suchlike, and a problem occurs with regard to communication quality at the one access point.
Therefore, in order to assure communication quality at access points (wireless devices), an access control device, wireless device and network are sought which can share out transfer destinations of client terminals (wireless terminals) assigned to the access points (wireless devices), can efficiently utilize an overall communication bandwidth of a network system, and can make communication volumes of respective usable wireless channels uniform.